2010 Peugeot 207 Turbo whistle

Id start by checking the tubes that go into ad out of the turbo. These are charge-air or intercooler tubes. Sometimes the rubber connector hoses get holes in them or they simply come loose. You may also have a stuck waste gate or variable turbo vane. Take the tube coming from the air box off the turbo an see if you can grab the inner nut in the middle of the impellor and wiggle it. Any movement can mean a worn out turbo. Also look for evidence of dust or dirt in the throat going up to the impellor. That means you've got dirt/dust getting by the air filter.